Abstract

A silica-based highly acoustically-anti-guiding optical fiber, fabricated using a molten core approach employing spinel (MgAl2O4) for the first time, is presented. To our knowledge, this is the first truly single mode optical fiber fabricated from a precursor crystal. It is shown that MgO increases the acoustic velocity when added to silica (some physical parameters of MgO are identified) and that the Brillouin gain in the core is less than one third that in the cladding in one of the fibers. This results from a massive acoustic waveguide attenuation term that broadens the spectrum to well over 200 MHz. For the first time, to the best of our knowledge, this also enabled the validation of the intrinsic Brillouin line-width (~20 MHz) of pure silica in fiber form via a direct measurement.

Figures (4)

(a) An end-on view of Fiber A; similar results were obtained for Fiber B (see Table 1 for details). (b) Example of a splice of a segment of SpDF (left-side of image) to standard telecom fiber (right-side of image). High-quality splices were achieved utilizing a standard splice routine.

The Brillouin spectrum (blue) from spinel fibers A and B are fitted with a curve (orange), which is composed of a superposition of Lorentzian curves (dashed). The small peak near 11.15 GHz is the second-order acoustic mode from the apparatus fiber.